(a) Field
The present invention relates to a method of providing hybrid automatic repeat request (HARQ) feedback information. More particularly, the present invention relates to a method of providing configuration information of hybrid automatic repeat request (HARQ) feedback regions of a sub-frame, that is, the number of feedback regions in a time division duplex (TDD) mode.
(b) Description of Related Art
A wideband wireless access system is a next generation communication method of supporting hybrid automatic repeat request (HARQ) in which forward error correction (FEC) and automatic repeat request (ARQ) are combined with each other as an error compensation technique for securing reliability of communications with high speed data packet transmission and a small amount of delay.
In the wireless access system, a duplexing communication method is divided into a frequency division duplex (FDD) transmission mode method and a time division duplex (TDD) transmission mode method. The FDD transmission mode method distinguishes upward and downward transmitting and receiving resources by frequency to support bidirectional communications of uplink and downlink. The TDD transmission mode method distinguishes upward and downward transmitting and receiving resources by time to support bidirectional communications of uplink and downlink.
In the HARQ technique, a receiver decodes a data packet received by a physical layer to determine whether an error is detected, and transmits an acknowledgement (ACK) signal as a response signal when it is determined that the error is not generated to inform a transmitter that the data packet is successfully received. However, the receiver decodes the received data packet and transmits a negative acknowledgement (NACK) signal as a response signal when it is determined that an error is detected to inform the transmitter that the error is detected. The transmitter may re-transmit the data packet when the NACK signal is received.
The HARQ technique is divided into a synchronous HARQ technique and an asynchronous HARQ technique in accordance with transmission timing of a retransmitted packet. In the synchronous HARQ technique, a transmission point in time of the retransmitted packet with respect to an initially transmitted packet is uniformized. In the asynchronous HARQ technique, the transmission point in time of the retransmitted packet with respect to an initially transmitted packet is determined by a scheduler of a base station.
In addition, the HARQ technique is divided into an adaptive HARQ technique and a non-adaptive HARQ technique in accordance with whether an amount and a position of an allocated resource are changed. In the adaptive HARQ technique, the amount and position of the allocated resource may be changed. In the non-adaptive HARQ technique, the amount and position of the allocated resource are fixed.
In order to reduce signaling overhead in accordance with a control signal such as resource allocation information, it is effective to use a synchronous and non-adaptive HARQ technique. However, when the signaling overhead is not considered, it may be effective to use an asynchronous and adaptive HARQ technique with a scheduling gain.
A high scheduling gain and a high speed data transmission effect may be obtained by appropriately mixing the synchronous and asynchronous HARQ techniques and the adaptive and non-adaptive HARQ techniques, and using small signaling overhead.
When a terminal uses the synchronous HARQ technique for uplink, in order to transmit a HARQ packet to uplink, resource must be allocated by a downlink control signal from a base station. That is, the terminal receives an uplink transmission resource from the downlink control signal of the base station and transmits the HARQ packet to a designated position (a slot or a sub-frame). In addition, the base station transmits ACK feedback of the downlink as a HARQ feedback signal when the HARQ packet is successfully received without an error, and transmits NACK feedback of the downlink as a HARQ feedback signal when the HARQ packet is not received. At this time, the terminal retransmits a packet at a previously allocated designated point in time when the NACK feedback is received as the HARQ feedback signal.
In the TDD transmission mode divided into uplink and downlink, one frame may consist of at least one sub-frame with respect to uplink and downlink. A ratio between the number of sub-frames allocated to uplink and the number of sub-frames allocated to downlink may vary in accordance with a type of a frame structure. For example, when the number of sub-frames that form one frame is 6, 7, or 8, a ratio between the number of sub-frames allocated to uplink and the number of sub-frames allocated to downlink may be 3:3, 4:2, 2:4, 5:2, 3:4, 4:3, 2:5, 6:2, 5:3, 4:4, 3:5, or 2:6, and one of the above frame structures may be selected.
The downlink or every sub-frame of the downlink has at least one HARQ feedback region, and HARQ feedback is allocated to a corresponding HARQ feedback region.
The number of HARQ feedback regions may vary every sub-frame in accordance with the ratio between the number of sub-frames allocated to uplink and the number of sub-frames allocated to downlink. When the number of sub-frames allocated to uplink is equal to the number of sub-frames allocated to downlink, one HARQ feedback region may exist in each of the uplink and downlink sub-frames. On the other hand, when the number of sub-frames allocated to uplink and downlink varies, the number of HARQ feedback regions may vary every downlink sub-frame and the number of HARQ feedback regions may vary every uplink sub-frame.
That is, the number of HARQ feedback regions in each of the downlink and uplink sub-frames may be determined by a correlation among the downlink and uplink sub-frames, downlink, and the number of downlink sub-frames. Therefore, a base station and a terminal store information on the HARQ feedback regions in accordance with the ratio between the number of sub-frames allocated to uplink and the number of sub-frames allocated to downlink in a memory in the form of a lookup table, and provide the information on the HARQ feedback regions using the lookup table. The base station and the terminal confirm the numbers of HARQ feedback regions of the downlink and uplink sub-frames in accordance with the numbers of downlink and uplink sub-frames that form one frame using the lookup table, and allocate the HARQ feedback regions to the downlink and uplink sub-frames, respectively.
However, in a method of providing information on the HARQ feedback regions using the lookup table, a memory for storing the lookup table is required and it is difficult to immediately support an added frame structure. In addition, in order for the base station and the terminal to support various added frame structures, information on HARQ feedback regions of an added frame structure must be updated in the lookup table by changing a program.